Biology PublicationsCopyright (c) 2016 Western University All rights reserved.http://ir.lib.uwo.ca/biologypub
Recent documents in Biology Publicationsen-usFri, 11 Nov 2016 13:05:57 PST3600Tomato Whole Genome Transcriptional Response to Tetranychus urticae Identifies Divergence of Spider Mite-Induced Responses Between Tomato and Arabidopsishttp://ir.lib.uwo.ca/biologypub/63
http://ir.lib.uwo.ca/biologypub/63Mon, 07 Nov 2016 09:10:54 PST
The two-spotted spider mite Tetranychus urticae is one of the most significant mite pests in agriculture, feeding on more than 1,100 plant hosts, including model plants Arabidopsis thaliana and tomato, Solanum lycopersicum. Here, we describe timecourse tomato transcriptional responses to spider mite feeding and compare them with Arabidopsis in order to determine conserved and divergent defense responses to this pest. To refine the involvement of jasmonic acid (JA) in mite-induced responses and to improve tomato Gene Ontology annotations, we analyzed transcriptional changes in the tomato JA-signaling mutant defenseless1 (def-1) upon JA treatment and spider mite herbivory. Overlay of differentially expressed genes (DEG) identified in def-1 onto those from the timecourse experiment established that JA controls expression of the majority of genes differentially regulated by herbivory. Comparison of defense responses between tomato and Arabidopsis highlighted 96 orthologous genes (of 2,133 DEG) that were recruited for defense against spider mites in both species. These genes, involved in biosynthesis of JA, phenylpropanoids, flavonoids, and terpenoids, represent the conserved core of induced defenses. The remaining tomato DEG support the establishment of tomato-specific defenses, indicating profound divergence of spider mite-induced responses between tomato and Arabidopsis.
]]>
Catherine Martel et al.Metabolism of brain cortex and cardiac muscle mitochondria in hibernating 13-lined ground squirrels Ictidomys tridecemlineatus.http://ir.lib.uwo.ca/biologypub/62
http://ir.lib.uwo.ca/biologypub/62Tue, 25 Oct 2016 14:03:57 PDT
During bouts of torpor, mitochondrial metabolism is known to be suppressed in the liver and skeletal muscle of hibernating mammals. This suppression is rapidly reversed during interbout euthermic (IBE) phases, when whole-animal metabolic rate and body temperature (T(b)) return spontaneously to euthermic levels. Such mitochondrial suppression may contribute significantly to energy savings, but the capacity of other tissues to suppress mitochondrial metabolism remains unclear. In this study we compared the metabolism of mitochondria from brain cortex and left ventricular cardiac muscle between animals sampled while torpid (stable T(b) near 5°C) and in IBE (stable T(b) near 37°C). Instead of isolating mitochondria using the traditional methods of homogenization and centrifugation, we permeabilized tissue slices with saponin, allowing energetic substrates and inhibitors to access mitochondria. No significant differences in state 3 or state 4 respiration were observed between torpor and IBE in either tissue. In general, succinate produced the highest oxidation rates followed by pyruvate and then glutamate, palmitoyl carnitine, and β-hydroxybutyrate. These findings suggest that there is no suppression of mitochondrial metabolism or change in substrate preference in these two tissues despite the large changes in whole-animal metabolism seen between torpor and IBE.
]]>
Kirsten Gallagher et al.AnimalsCell RespirationCerebral CortexHeart VentriclesHibernationManitobaMitochondriaMitochondria, MuscleMyocardiumReactive Oxygen SpeciesSaponinsSciuridaeSeasonsSelective mobilization of saturated fatty acids in isolated adipocytes of hibernating 13-lined ground squirrels Ictidomys tridecemlineatus.http://ir.lib.uwo.ca/biologypub/61
http://ir.lib.uwo.ca/biologypub/61Tue, 25 Oct 2016 14:03:53 PDT
Fatty acids are not mobilized from adipocyte triacylglycerols uniformly but rather some are preferentially mobilized while others are preferentially retained. In many vertebrate species, the pattern of differential mobilization is determined by the physical and chemical properties of each fatty acid. Fatty acids with shorter chains and more double bonds tend to be more readily mobilized than others, a pattern observed both in whole-animal studies and in isolated adipocytes. Several hibernating species seem to break this pattern, however, and retain 18:2ω6 (linoleic acid) while mobilizing saturated fatty acids such as 18:0. We sought to confirm this pattern in adipocytes of a hibernator, the 13-lined ground squirrel Ictidomys tridecemlineatus, and to investigate mobilization patterns for the first time at hibernation temperature. We isolated adipocytes from summer active and winter torpid squirrels and incubated them with 1 μM norepinephrine at 4°C (7 h) and 37°C (90 min). We measured the proportion of each fatty acid in the adipose tissue and in the buffer at the end of incubation. Patterns of mobilization were similar in both seasons and incubation temperatures. Saturated fatty acids (18:0 and 16:0) were highly mobilized relative to the average, while some unsaturated fatty acids (notably, 18:1ω9 and 18:2ω6) were retained. We conclude that hibernators have unique mechanisms at the level of adipose tissue that preferentially mobilize saturated fatty acids. Additionally, we found that adipocytes from hibernating squirrels produced more glycerol than those from summer squirrels (regardless of temperature), indicating a higher lipolytic capacity in hibernating squirrels.
]]>
Edwin R Price et al.AdipocytesAnimalsFatty AcidsFlame IonizationGas Chromatography-Mass SpectrometryHibernationLipid MobilizationManitobaSciuridaeSeasonsTemperatureRegulation of succinate-fuelled mitochondrial respiration in liver and skeletal muscle of hibernating thirteen-lined ground squirrels.http://ir.lib.uwo.ca/biologypub/60
http://ir.lib.uwo.ca/biologypub/60Tue, 25 Oct 2016 14:03:50 PDT
Hibernating ground squirrels (Ictidomys tridecemlineatus) alternate between two distinct metabolic states throughout winter: torpor, during which metabolic rate (MR) and body temperature (Tb) are considerably suppressed, and interbout euthermia (IBE), during which MR and Tb briefly return to euthermic levels. Previous studies showed suppression of succinate-fuelled respiration during torpor in liver and skeletal muscle mitochondria; however, these studies used only a single, saturating succinate concentration. Therefore, they could not address whether mitochondrial metabolic suppression occurs under physiological substrate concentrations or whether differences in the kinetics of mitochondrial responses to changing substrate concentration might also contribute to mitochondrial metabolic regulation during torpor. The present study confirmed that succinate oxidation is reduced during torpor in liver and skeletal muscle at 37 and 10°C over a 100-fold range of succinate concentrations. At 37°C, this suppression resulted from inhibition of succinate dehydrogenase (SDH), which had a greater affinity for oxaloacetate (an SDH inhibitor) during torpor. At 10°C, SDH was not inhibited, suggesting that SDH inhibition initiates but does not maintain mitochondrial suppression during torpor. Moreover, in both liver and skeletal muscle, mitochondria from torpid animals maintained relatively higher respiration rates at low succinate concentrations, which reduces the extent of energy savings that can be achieved during torpor, but may also maintain mitochondrial oxidative capacity above some lower critical threshold, thereby preventing cellular and/or mitochondrial injury during torpor and facilitating rapid recruitment of oxidative capacity during arousal.
]]>
Jason C L Brown et al.AnimalsCell RespirationFemaleHibernationKineticsLiverMitochondria, LiverMitochondria, MuscleMuscle, SkeletalOxaloacetic AcidSciuridaeSuccinate DehydrogenaseSuccinic AcidTemperatureAdaptations to hibernation in lung surfactant composition of 13-lined ground squirrels influence surfactant lipid phase segregation properties.http://ir.lib.uwo.ca/biologypub/59
http://ir.lib.uwo.ca/biologypub/59Tue, 25 Oct 2016 14:03:46 PDT
Pulmonary surfactant lines the entire alveolar surface, serving primarily to reduce the surface tension at the air-liquid interface. Surfactant films adsorb as a monolayer interspersed with multilayers with surfactant lipids segregating into different phases or domains. Temperature variation, which influences lipid physical properties, affects both the lipid phase segregation and the surface activity of surfactants. In hibernating animals, such as 13-lined ground squirrels, which vary their body temperature, surfactant must be functional over a wide range of temperatures. We hypothesised that surfactant from the 13-lined ground squirrel, Ictidomys tridecemlineatus, would undergo appropriate lipid structural re-arrangements at air-water interfaces to generate phase separation, sufficient to attain the low surface tensions required to remain stable at both low and high body temperatures. Here, we examined pressure-area isotherms at 10, 25 and 37°C and found that surfactant films from both hibernating and summer-active squirrels reached their highest surface pressure on the Wilhelmy-Langmuir balance at 10°C. Epifluorescence microscopy demonstrated that films of hibernating squirrel surfactant display different lipid micro-domain organisation characteristics than surfactant from summer-active squirrels. These differences were also reflected at the nanoscale as determined by atomic force microscopy. Such re-arrangement of lipid domains in the relatively more fluid surfactant films of hibernating squirrels may contribute to overcoming collapse pressures and support low surface tension during the normal breathing cycle at low body temperatures.
]]>
Lakshmi N M Suri et al.Adaptation, PhysiologicalAnimalsHibernationLipidsMicroscopy, Atomic ForcePulmonary SurfactantsSciuridaeSurface PropertiesSurface TensionTemperatureThe effects of hibernation on the contractile and biochemical properties of skeletal muscles in the thirteen-lined ground squirrel, Ictidomys tridecemlineatus.http://ir.lib.uwo.ca/biologypub/58
http://ir.lib.uwo.ca/biologypub/58Tue, 25 Oct 2016 14:03:43 PDT
Hibernation is a crucial strategy of winter survival used by many mammals. During hibernation, thirteen-lined ground squirrels, Ictidomys tridecemlineatus, cycle through a series of torpor bouts, each lasting more than a week, during which the animals are largely immobile. Previous hibernation studies have demonstrated that such natural models of skeletal muscle disuse cause limited or no change in either skeletal muscle size or contractile performance. However, work loop analysis of skeletal muscle, which provides a realistic assessment of in vivo power output, has not previously been undertaken in mammals that undergo prolonged torpor during hibernation. In the present study, our aim was to assess the effects of 3 months of hibernation on contractile performance (using the work loop technique) and several biochemical properties that may affect performance. There was no significant difference in soleus muscle power output-cycle frequency curves between winter (torpid) and summer (active) animals. Total antioxidant capacity of gastrocnemius muscle was 156% higher in torpid than in summer animals, suggesting one potential mechanism for maintenance of acute muscle performance. Soleus muscle fatigue resistance was significantly lower in torpid than in summer animals. Gastrocnemius muscle glycogen content was unchanged. However, state 3 and state 4 mitochondrial respiration rates were significantly suppressed, by 59% and 44%, respectively, in mixed hindlimb skeletal muscle from torpid animals compared with summer controls. These findings in hindlimb skeletal muscles suggest that, although maximal contractile power output is maintained in torpor, there is both suppression of ATP production capacity and reduced fatigue resistance.
]]>
Rob S James et al.Adenosine TriphosphateAnalysis of VarianceAnimalsAntioxidantsBiomechanical PhenomenaCell RespirationFemaleGlycogenHibernationMaleMuscle ContractionMuscle, SkeletalSciuridaeSeasonsTime FactorsChanges in the mitochondrial phosphoproteome during mammalian hibernation.http://ir.lib.uwo.ca/biologypub/57
http://ir.lib.uwo.ca/biologypub/57Tue, 25 Oct 2016 14:03:39 PDT
Mammalian hibernation involves periods of substantial suppression of metabolic rate (torpor) allowing energy conservation during winter. In thirteen-lined ground squirrels (Ictidomys tridecemlineatus), suppression of liver mitochondrial respiration during entrance into torpor occurs rapidly (within 2 h) before core body temperature falls below 30°C, whereas reversal of this suppression occurs slowly during arousal from torpor. We hypothesized that this pattern of rapid suppression in entrance and slow reversal during arousal was related to changes in the phosphorylation state of mitochondrial enzymes during torpor catalyzed by temperature-dependent kinases and phosphatases. We compared mitochondrial protein phosphorylation among hibernation metabolic states using immunoblot analyses and assessed how phosphorylation related to mitochondrial respiration rates. No proteins showed torpor-specific changes in phosphorylation, nor did phosphorylation state correlate with mitochondrial respiration. However, several proteins showed seasonal (summer vs. winter) differences in phosphorylation of threonine or serine residues. Using matrix-assisted laser desorption/ionization-time of flight/time of flight mass spectrometry, we identified three of these proteins: F1-ATPase α-chain, long chain-specific acyl-CoA dehydrogenase, and ornithine transcarbamylase. Therefore, we conclude that protein phosphorylation is likely a mechanism involved in bringing about seasonal changes in mitochondrial metabolism in hibernating ground squirrels, but it seems unlikely to play any role in acute suppression of mitochondrial metabolism during torpor.
]]>
Dillon J Chung et al.AnimalsBody TemperatureElectrophoresis, Gel, Two-DimensionalFemaleHibernationMaleMammalsMitochondria, LiverMitochondrial ProteinsOxygen ConsumptionPhosphoproteinsPhosphorylationProteomeProteomicsSciuridaeSeasonsSerineSpectrometry, Mass, Matrix-Assisted Laser Desorption-IonizationThreonineIdentification, expression, and taxonomic distribution of alternative oxidases in non-angiosperm plants.http://ir.lib.uwo.ca/biologypub/56
http://ir.lib.uwo.ca/biologypub/56Tue, 25 Oct 2016 14:03:35 PDT
Alternative oxidase (AOX) is a terminal ubiquinol oxidase present in the respiratory chain of all angiosperms investigated to date, but AOX distribution in other members of the Viridiplantae is less clear. We assessed the taxonomic distribution of AOX using bioinformatics. Multiple sequence alignments compared AOX proteins and examined amino acid residues involved in AOX catalytic function and post-translational regulation. Novel AOX sequences were found in both Chlorophytes and Streptophytes and we conclude that AOX is widespread in the Viridiplantae. AOX multigene families are common in non-angiosperm plants and the appearance of AOX1 and AOX2 subtypes pre-dates the divergence of the Coniferophyta and Magnoliophyta. Residues involved in AOX catalytic function are highly conserved between Chlorophytes and Streptophytes, while AOX post-translational regulation likely differs in these two lineages. We demonstrate experimentally that an AOX gene is present in the moss Physcomitrella patens and that the gene is transcribed. Our findings suggest that AOX will likely exert an influence on plant respiration and carbon metabolism in non-angiosperms such as green algae, bryophytes, liverworts, lycopods, ferns, gnetophytes, and gymnosperms and that further research in these systems is required.
]]>
Karina Neimanis et al.Amino Acid SequenceBase SequenceBinding SitesComputational BiologyDatabases, GeneticEvolution, MolecularIronMitochondrial ProteinsMolecular Sequence DataOxidoreductasesPlant ProteinsPlantsProtein BindingSequence AlignmentViridiplantaeAre long chain acyl CoAs responsible for suppression of mitochondrial metabolism in hibernating 13-lined ground squirrels?http://ir.lib.uwo.ca/biologypub/55
http://ir.lib.uwo.ca/biologypub/55Tue, 25 Oct 2016 14:03:31 PDT
Hibernation in 13-lined ground squirrels (Ictidomys tridecemlineatus) is associated with a substantial suppression of whole-animal metabolism. We compared the metabolism of liver mitochondria isolated from torpid ground squirrels with those from interbout euthermic (IBE; recently aroused from torpor) and summer euthermic conspecifics. Succinate-fuelled state 3 respiration, calculated relative to mitochondrial protein, was suppressed in torpor by 48% and 44% compared with IBE and summer, respectively. This suppression remains when respiration is expressed relative to cytochrome c oxidase activity. We hypothesized that this suppression was caused by inhibition of succinate transport at the dicarboxylate transporter (DCT) by long-chain fatty acyl CoAs that may accumulate during torpor. We predicted, therefore, that exogenous palmitoyl CoA would inhibit respiration in IBE more than in torpor. Palmitoyl CoA inhibited respiration ~70%, in both torpor and IBE. The addition of carnitine, predicted to reverse palmitoyl CoA suppression by facilitating its transport into the mitochondrial matrix, did not rescue the respiration rates in IBE or torpor. Liver mitochondrial activities of carnitine palmitoyl transferase did not differ among IBE, torpor and summer animals. Although palmitoyl CoA inhibits succinate-fuelled respiration, this suppression is likely not related exclusively to inhibition of the DCT, and may involve additional mitochondrial transporters such as the adenine-nucleotide transporter.
]]>
Alex N Cooper et al.Acyl Coenzyme AAnimalsElectron Transport Complex IVHibernationMitochondria, LiverMitochondrial ProteinsOxygen ConsumptionSciuridaeSeasonsSubstrate-specific changes in mitochondrial respiration in skeletal and cardiac muscle of hibernating thirteen-lined ground squirrels.http://ir.lib.uwo.ca/biologypub/54
http://ir.lib.uwo.ca/biologypub/54Tue, 25 Oct 2016 14:03:27 PDT
During torpor, the metabolic rate (MR) of thirteen-lined ground squirrels (Ictidomys tridecemlineatus) is considerably lower relative to euthermia, resulting in part from temperature-independent mitochondrial metabolic suppression in liver and skeletal muscle, which together account for ~40% of basal MR. Although heart accounts for very little (
]]>
Jason C L Brown et al.AnimalsCell RespirationCitrate (si)-SynthaseFemaleHibernationMaleMitochondria, MuscleMuscle, SkeletalMyocardiumSciuridaeSuccinate DehydrogenaseParallel ionoregulatory adjustments underlie phenotypic plasticity and evolution of Drosophila cold tolerance.http://ir.lib.uwo.ca/biologypub/53
http://ir.lib.uwo.ca/biologypub/53Tue, 25 Oct 2016 14:03:23 PDT
Low temperature tolerance is the main predictor of variation in the global distribution and performance of insects, yet the molecular mechanisms underlying cold tolerance variation are poorly known, and it is unclear whether the mechanisms that improve cold tolerance within the lifetime of an individual insect are similar to those that underlie evolved differences among species. The accumulation of cold-induced injuries by hemimetabolous insects is associated with loss of Na(+) and K(+) homeostasis. Here we show that this model holds true for Drosophila; cold exposure increases haemolymph [K(+)] in D. melanogaster, and cold-acclimated flies maintain low haemolymph [Na(+)] and [K(+)], both at rest and during a cold exposure. This pattern holds across 24 species of the Drosophila phylogeny, where improvements in cold tolerance have been consistently paired with reductions in haemolymph [Na(+)] and [K(+)]. Cold-acclimated D. melanogaster have low activity of Na(+)/K(+)-ATPase, which may contribute to the maintenance of low haemolymph [Na(+)] and underlie improvements in cold tolerance. Modifications to ion balance are associated with both phenotypic plasticity within D. melanogaster and evolutionary differences in cold tolerance across the Drosophila phylogeny, which suggests that adaptation and acclimation of cold tolerance in insects may occur through similar mechanisms. Cold-tolerant flies maintain haemolymph osmolality despite low haemolymph [Na(+)] and [K(+)], possibly through modest accumulations of organic osmolytes. We propose that this could have served as an evolutionary route by which chill-susceptible insects developed more extreme cold tolerance strategies.
]]>
Heath A MacMillan et al.AcclimatizationAdaptation, PhysiologicalAnimalsBiological EvolutionCold TemperatureDrosophila melanogasterHemolymphPhylogenySodium-Potassium-Exchanging ATPaseWater-Electrolyte BalanceSaponin-Permeabilization is Not a Viable Alternative to Isolated Mitochondria for Assessing Oxidative Metabolism in Hibernationhttp://ir.lib.uwo.ca/biologypub/52
http://ir.lib.uwo.ca/biologypub/52Tue, 25 Oct 2016 14:03:19 PDT
Saponin permeabilization of tissue slices is increasingly popular for characterizing mitochondrial function largely because it is fast, easy, requires little tissue and leaves much of the cell intact. This technique is well described for mammalian muscle and brain, but not for liver. We sought to evaluate how saponin permeabilization reflects aspects of liver energy metabolism typically assessed in isolated mitochondria. We studied the ground squirrel (Ictidomys tridecemlineatus Mitchell), a hibernating mammal that shows profound and acute whole-animal metabolic suppression in the transition from winter euthermia to torpor. This reversible metabolic suppression is also reflected in the metabolism of isolated liver mitochondria. In this study we compared euthermic and torpid animals using saponin permeabilized tissue and mitochondria isolated from the same livers. As previously demonstrated, isolated mitochondria have state 3 respiration rates, fueled by succinate, that are suppressed by 60-70% during torpor. This result holds whether respiration is standardized to mitochondrial protein, cytochrome a content or citrate synthase activity. In contrast, saponin-permeabilized liver tissue, show no such suppression in torpor. Neither citrate synthase activity nor VDAC content differ between torpor and euthermia, indicating that mitochondrial content remains constant in both permeabilized tissue and isolated mitochondria. In contrast succinate dehydrogenase activity is suppressed during torpor in isolated mitochondria, but not in permeabilized tissue. Mechanisms underlying metabolic suppression in torpor may have been reversed by the permeabilization process. As a result we cannot recommend saponin permeabilization for assessing liver mitochondrial function under conditions where acute changes in metabolism are known to occur.
]]>
Katherine E. Mathers et al.Regulation of mitochondrial metabolism during hibernation by reversible suppression of electron transport system enzymes.http://ir.lib.uwo.ca/biologypub/51
http://ir.lib.uwo.ca/biologypub/51Tue, 25 Oct 2016 14:03:15 PDT
Small hibernators cycle between periods of torpor, with body temperature (T b) approximately 5 °C, and interbout euthermia (IBE), where T b is approximately 37 °C. During entrance into a torpor bout liver mitochondrial respiration is rapidly suppressed by 70 % relative to IBE. We compared activities of electron transport system (ETS) complexes in intact liver mitochondria isolated from 13-lined ground squirrels (Ictidomys tridecemlineatus) sampled during torpor and IBE to investigate potential sites of this reversible metabolic suppression. Flux through complexes I-IV and II-IV was suppressed by 40 and 60 %, respectively, in torpor, while flux through complexes III-IV and IV did not differ between torpor and IBE. We also measured maximal enzyme activity of ETS enzymes in homogenized isolated mitochondria and whole liver tissue. In isolated mitochondria, activities of complexes I and II were significantly lower in torpor relative to IBE, but complexes III, IV, and V did not differ. In liver tissue, only activity of complex II was suppressed during torpor relative to IBE. Despite the significant differences in both ETS flux and maximal activity, the protein content of complexes I and II did not differ between torpor and IBE. These results suggest that the rapid, reversible suppression of mitochondrial metabolism is due to regulatory changes, perhaps by post-translational modification during entrance into a torpor bout, and not changes in ETS protein content.
]]>
Katherine E Mathers et al.Mitochondrial metabolism in hibernation and daily torpor: a review.http://ir.lib.uwo.ca/biologypub/50
http://ir.lib.uwo.ca/biologypub/50Thu, 20 Oct 2016 11:30:57 PDT
Hibernation and daily torpor involve substantial decreases in body temperature and metabolic rate, allowing birds and mammals to cope with cold environments and/or limited food. Regulated suppression of mitochondrial metabolism probably contributes to energy savings: state 3 (phosphorylating) respiration is lower in liver mitochondria isolated from mammals in hibernation or daily torpor compared to normothermic controls, although data on state 4 (non-phosphorylating) respiration are equivocal. However, no suppression is seen in skeletal muscle, and there is little reliable data from other tissues. In both daily torpor and hibernation, liver state 3 substrate oxidation is suppressed, especially upstream of electron transport chain complex IV. In hibernation respiratory suppression is reversed quickly in arousal even when body temperature is very low, implying acute regulatory mechanisms, such as oxaloacetate inhibition of succinate dehydrogenase. Respiratory suppression depends on in vitro assay temperature (no suppression is evident below approximately 30 degrees C) and (at least in hibernation) dietary polyunsaturated fats, suggesting effects on inner mitochondrial membrane phospholipids. Proton leakiness of the inner mitochondrial membrane does not change in hibernation, but this also depends on dietary polyunsaturates. In contrast proton leak increases in daily torpor, perhaps limiting reactive oxygen species production.
]]>
James F Staples et al.AnimalsBasal MetabolismBody TemperatureHibernationMitochondria, LiverMitochondrial MembranesRespirationMatching cellular metabolic supply and demand in energy-stressed animals.http://ir.lib.uwo.ca/biologypub/49
http://ir.lib.uwo.ca/biologypub/49Thu, 20 Oct 2016 11:26:25 PDT
Certain environmental stressors can impair cellular ATP production to the point of harming or even killing an animal. Some exceptional animals employ strategies that maintain the balance between ATP production and consumption, allowing them to tolerate prolonged exposure to stressors such as hypoxia and anoxia. Anoxia- and hypoxia-tolerant animals reduce ATP consumption by ion-motive ATPases while concomitant reductions in passive ion flux reduce the demand for ion pumping and maintain transmembrane ion gradients. Reductions in gene transcription and protein turnover decrease ATP demand in hibernating and hypoxia-tolerant animals. Proton leak uncouples mitochondrial substrate oxidation from ATP synthesis and accounts for a considerable proportion of cellular energy demand, but there is little evidence that the proton permeability of inner mitochondrial membranes decreases in animals that tolerate energy stress. Indeed in some cases proton leak increases, possibly reducing reactive oxygen species production. Because substrate oxidation is important to the control of cellular metabolism, the downregulation of ATP supply pathways contributes significantly to metabolic suppression under energy stress. Mechanisms that coordinate the downregulation of both ATP supply and demand pathways include AMP kinase and ATP-sensitive ion channels. Strategies employed by animals tolerant to one energy stress often convey "cross-tolerance" to completely different stresses.
]]>
James F Staples et al.Adenosine TriphosphateAnimalsAnoxiaEnergy MetabolismStress, PhysiologicalMetabolic Flexibility: Hibernation, Torpor, and Estivation.http://ir.lib.uwo.ca/biologypub/48
http://ir.lib.uwo.ca/biologypub/48Thu, 20 Oct 2016 11:16:10 PDT
Many environmental conditions can constrain the ability of animals to obtain sufficient food energy, or transform that food energy into useful chemical forms. To survive extended periods under such conditions animals must suppress metabolic rate to conserve energy, water, or oxygen. Amongst small endotherms, this metabolic suppression is accompanied by and, in some cases, facilitated by a decrease in core body temperature-hibernation or daily torpor-though significant metabolic suppression can be achieved even with only modest cooling. Within some ectotherms, winter metabolic suppression exceeds the passive effects of cooling. During dry seasons, estivating ectotherms can reduce metabolism without changes in body temperature, conserving energy reserves, and reducing gas exchange and its inevitable loss of water vapor. This overview explores the similarities and differences of metabolic suppression among these states within adult animals (excluding developmental diapause), and integrates levels of organization from the whole animal to the genome, where possible. Several similarities among these states are highlighted, including patterns and regulation of metabolic balance, fuel use, and mitochondrial metabolism. Differences among models are also apparent, particularly in whether the metabolic suppression is intrinsic to the tissue or depends on the whole-animal response. While in these hypometabolic states, tissues from many animals are tolerant of hypoxia/anoxia, ischemia/reperfusion, and disuse. These natural models may, therefore, serve as valuable and instructive models for biomedical research.
]]>
James F StaplesMetabolic suppression in mammalian hibernation: the role of mitochondria.http://ir.lib.uwo.ca/biologypub/47
http://ir.lib.uwo.ca/biologypub/47Wed, 19 Oct 2016 14:37:10 PDT
Hibernation evolved in some small mammals that live in cold environments, presumably to conserve energy when food supplies are low. Throughout the winter, hibernators cycle spontaneously between torpor, with low metabolism and near-freezing body temperatures, and euthermia, with high metabolism and body temperatures near 37°C. Understanding the mechanisms underlying this natural model of extreme metabolic plasticity is important for fundamental and applied science. During entrance into torpor, reductions in metabolic rate begin before body temperatures fall, even when thermogenesis is not active, suggesting active mechanisms of metabolic suppression, rather than passive thermal effects. Mitochondrial respiration is suppressed during torpor, especially when measured in liver mitochondria fuelled with succinate at 37°C in vitro. This suppression of mitochondrial metabolism appears to be invoked quickly during entrance into torpor when body temperature is high, but is reversed slowly during arousal when body temperature is low. This pattern may reflect body temperature-sensitive, enzyme-mediated post-translational modifications of oxidative phosphorylation complexes, for instance by phosphorylation or acetylation.
]]>
James F StaplesAnimalsCell RespirationHibernationMammalsMitochondriaIt Takes an Individual Plant to Raise a Community: TRFLP Analysis of the Rhizosphere Microbial Community of Two Pairs of High- and Low-Metal-Accumulating Plantshttp://ir.lib.uwo.ca/biologypub/46
http://ir.lib.uwo.ca/biologypub/46Mon, 29 Aug 2016 07:45:53 PDT
We used terminal restriction fragment length polymorphism (TRFLP) analysis to look at the microbial community profiles of the rhizosphere surrounding two pairs of high- and low-metal (Cd)-accumulating plants (Brassica and Triticum). Unexpectedly, the microbial community did not vary with soil type, time, plant type, or metal-accumulating ability of the plant. Instead, when a plant's metal-accumulating ability was well matched to the level of metal contamination in the soil, the microbial populations in the rhizosphere were different than those of the seed endophytes and bulk soil. Unmatched plants had the same microbial community as bulk soil. The plant interaction with the soil, therefore, is essential to forming the bacterial community in the rhizosphere.
]]>
Melanie P. Columbus et al.Does the Response of Insect Herbivores to Cadmium Depend on Their Feeding Strategy?http://ir.lib.uwo.ca/biologypub/45
http://ir.lib.uwo.ca/biologypub/45Mon, 29 Aug 2016 07:45:48 PDT
Phytoremediation has been proposed for the elimination of toxic metals in soil, yet little attention has been given to the performance of insects that feed on contaminant-tolerant plants. We tested the performance of two herbivores with different feeding behaviors, the cabbage looper, Trichoplusia ni, and the green peach aphid, Myzus persicae, reared on cadmium-tolerant Brassica juncea plants that contained different concentrations of cadmium. We also tested the performance of the aphid parasitoid Aphidius colemani developing in aphids reared on plants with different levels of cadmium. The hypothesis tested was that the chewing insect would be more negatively affected than the sucking insect, because of the localization of cadmium within the host plant, and that the aphid parasitoid would not be affected. We also compared the performance of T. ni on artificial diet with different levels of cadmium. Neither the phloem-feeding aphid nor its parasitoid was affected by cadmium in the host plant. The effects of cadmium on the foliage-feeding cabbage looper varied, with negative effects on development observed in experiments with artificial diet but not in those using natural host plants. These data, together with information available in the literature, support the idea that the effects of toxic metals present in a host plant may be influenced by a herbivore’s feeding strategy. However, a wide range of chewing and sucking species needs to be tested to confirm this hypothesis.
]]>
Joanna K. Konopka et al.Reduced Translocation of Cadmium from Roots Is Associated with Increased Production of Phytochelatins and Their Precursorshttp://ir.lib.uwo.ca/biologypub/44
http://ir.lib.uwo.ca/biologypub/44Mon, 08 Aug 2016 12:11:59 PDT
Cadmium (Cd) is a non-essential trace element and its environmental concentrations are approaching toxic levels, especially in some agricultural soils. Understanding how and where Cd is stored in plants is important for ensuring food safety. In this study, we examined two plant species that differ in the distribution of Cd among roots and leaves. Lettuce and barley were grown in nutrient solution under two conditions: chronic (4 weeks) exposure to a low, environmentally relevant concentration (1.0 μM) of Cd and acute (1 h) exposure to a high concentration (5.0 mM) of Cd. Seedlings grown in solution containing 1.0 μM CdCl2 did not show symptoms of toxicity and, at this concentration, 77% of the total Cd was translocated to leaves of lettuce, whereas only 24% of the total Cd was translocated to barley leaves. We tested the hypothesis that differential accumulation of Cd in roots and leaves is related to differential concentrations of phytochelatins (PCs), and its precursor peptides. The amounts of PCs and their precursor peptides in the roots and shoots were measured using HPLC. Each of PC2–4 was synthesized in the barley root upon chronic exposure to Cd and did not increase further upon acute exposure. In the case of lettuce, no PCs were detected in the root given either Cd treatment. The high amounts of PCs produced in barley root could have contributed to preferential retention of Cd in barley roots.
]]>
Mst. Fardausi Akhter et al.